A coordinated multi-point (CoMP) transmission technology is an important technology in a fourth generation mobile communications system, and plays an important role in greatly improving spectrum efficiency. The CoMP transmission technology simultaneously provides a data transmission service for one or multiple user equipments (UEs) at multiple access points that are geographically separate from each other, where the multiple access points may belong to one or different NodeBs.
For the CoMP transmission technology, before performing CoMP transmission or reception, a NodeB needs to select an access point (set) for a UE and schedule time/frequency resources used for transmission. These operations need to refer to channel state information (CSI) between the UE and the access point (set). The CSI includes a channel quality indicator (CQI), a rank indicator (RI), and a precoding matrix indicator (PMI). In a single-point transmission system of the prior art, the UE transmits an uplink reference signal to the NodeB through an uplink band, and therefore, the NodeB may obtain the CSI of an uplink channel according to the received uplink reference signal; for downlink CSI, the NodeB transmits a downlink reference signal, and after receiving the downlink reference signal of the NodeB, the UE may obtain the downlink CSI, and feed back the obtained downlink CSI to the NodeB through the uplink band.
If the method in the single-point transmission system of the prior art is also used in a CoMP transmission system, huge signaling overheads are caused. Because in the CoMP transmission system, multiple NodeBs transmit downlink reference signals, and after obtaining the downlink CSI according to a received downlink reference signal of each NodeB, the UE feeds back the obtained downlink CSI to each NodeB through the uplink band, the signaling overheads of the uplink feedback CSI are huge, resulting in huge signaling overheads of the whole system and affecting the spectrum efficiency of the whole system.